btrfs: mark resumed async balance as writing

When btrfs balance is interrupted with umount, the background balance
resumes on the next mount. There is a potential deadlock with FS freezing
here like as described in commit 26559780b953 ("btrfs: zoned: mark
relocation as writing"). Mark the process as sb_writing to avoid it.

Reviewed-by: Filipe Manana <fdmanana@suse.com>
CC: stable@vger.kernel.org # 4.9+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 2cfbc74a3b4ee198e41d425bab82e98c2d6ef7e0..a8cc736731fdbed9e0b7539d781dacae25b29632 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4430,10 +4430,12 @@ static int balance_kthread(void *data)
        struct btrfs_fs_info *fs_info = data;
        int ret = 0;
 
+       sb_start_write(fs_info->sb);
        mutex_lock(&fs_info->balance_mutex);
        if (fs_info->balance_ctl)
                ret = btrfs_balance(fs_info, fs_info->balance_ctl, NULL);
        mutex_unlock(&fs_info->balance_mutex);
+       sb_end_write(fs_info->sb);
 
        return ret;
 }